It is known, especially in the area of watch casings, that a casing is coated with a hard coating, which shields it from corrosion and scratching, or from wear and tear due to contact of the casing with external objects, or the clothes of the watch wearer. For instance, European patent application No. 0 038 294 and Swiss patent application No. 631040G pertain to hard titanium nitride-based coatings, which display, in addition to their hardness, the advantage of displaying a color very close to that of gold.
However, even though the coating as obtained displays very good resistance to wear and tear, their withstanding of shocks, for instance against hard surfaces, is not entirely satisfactory. Indeed, because the coatings which are applied are relatively thin, about several dozen microns, the hardness of the coated part is roughly that of the substrate, which can be brass or steel, and if a dent in the substrate occurs, such can lead to deterioration of the hard coating, and of the appearance of the part.
In order to remedy the above disadvantage, a substrate that is made from a hard material, can be employed. However, the cost price of such an item and its tooling prior to coating become prohibitive, thereby detracting from its potential marketability.